A prior art cleaner for a conveyor belt is disclosed in U.S. Pat. No. 3,841,470 wherein the conveyor belt includes a plurality of cleaner means disposed thereon in the transverse direction of the conveyor belt at the return side of the same. Each cleaner means has a scraping portion thereof which intends to come into contact with the belt surface, while all of which are arranged in linear relationship. More specifically, a scraper having, at uppermost end, a scraping portion thereof comprising of tip members is yieldingly supported by a resilient member so that the scraping portion thereof becomes in contact with the belt surface under pressure by the resilience of the resilient member.
It is known that an endless conveyor belt, which is fitted for running in a circle between a drive pulley and an idler pulley, is supported on the forward side thereof by a plurality of guide rollers arranged at "trough" angles so as to be formed in a bow-like cross sectional shape in order to carry the transferring material in a stable manner. In other words, on the forward side of the running belt transferring the material thereon forward, the belt is supported so that the lengthwisely extending central region thereof can arcuately be deflected downward. The transferring materials are consecutively transferred generally on the central region of the belt, which will result in intensive wear on the central region of the belt surface rather than on both sides regions of the same.
Because of its tendency to deflection (termed generally as a "trough" tendency), the belt is deflected upward at a point midway between the side ends thereof thus to form an arch shape in cross section on the return side of the belt where the belt runs backward opposite to the forward direction thereof after discharging the transferring material therefrom. In such an arrangement of the known cleaner, the scraping portions of the cleaner means arranged in linear relationship are prevented from matching the belt surface when coming into close contact with the same. More specifically, there is a clearance between the scraping portions arranged linearly in said cleaner and the central region of the belt. The clearance becomes greater when the amount of wear on the central region of the belt surface is increased. Consequently, it will appear that the leavings of material on the central region of the belt surface cannot positively be scraped off by the scraping portions of the cleaner. Since the leavings of material adhered to the belt are substantially greater in amount at the lengthwisely extending central region of the belt surface than the side region of the same, some of the scraping portions disposed in the center get worn intensively in proportion to the amount of scraped material. This allows the clearance between the centrally mounted scraping portions and the belt surface to become greater gradually.
Each of the cleaner means has a scraper thereon which is supported yieldingly by the resilient member thus to be biased independently. When one of the scrapers is tilted laterally, a mass of the scraped material becomes trapped between the scraper and its adjacent scraper. This prevents the adjacent scraper from being biased independently, which will result in a stop of the returning movement of the scraping portion of the scraper from its biased position to its rest position for coming into contact with the belt surface.
Under the circumstances, an improved type of belt cleaner was developed by Nippon Tsusho Kabushiki Kaisha and is now sold under the product name "U-Type Cleaner" to which European Patent Nos. 0289659B1 and 0338118B1 (hereinafter referred to as the first EP and the second EP respectively) have granted.
In the cleaner for a conveyor belt according to the first EP, the scraper is adjustably supported for rotary displacement about the axis extending in the transverse direction of the belt and has the scraping portion thereon which intends to be in contact with the belt surface and is outwardly deflected a maximum from the common axis at a point midway between the side ends of the belt. Accordingly, when the scraper is turned upward about the axis to its standing position, the scraping portion thereof will arch its central region as lifted upward. This allows the scraping portion of the scraper to remain in close contact with the belt surface without clearance even if either the belt is trough-shaped in cross section or the lengthwisely extending central region of the belt surface gets worn, whereby the leavings on the belt surface will be scraped off in an optimum manner.
While according to the second EP, the scraper is formed of belt-like shape by a resilient board in which support members are embedded in a row, said resilient board comprises a cover wall extending integrally along over the aligned support members and covering the surfaces thereof, hinge portions connecting each two adjoined support members flexibly with each other so as to allow the scraper to be bent in a curved form thereby but not to allow the support members to separate with each other. The holder provides holding means which holds said scraper in its curved form via said hinge portions to deflect a maximum at a point midway between both ends of the belt from an axis extending transversely of the belt, the scraper is resiliently held by the holding means via said cover wall of the resilient board. The scraper is flexible to match the arcuate shape of the holding means in the holder. It is thus unnecessary for the scraper to have a shape corresponding to the arcuate shape of the holding means, which facilitates its fabrication.
However, according to the belt cleaner disclosed in the second EP, when the scraper scrapes the leavings of material on the conveyor belt, the leavings of material scraped and dropping down accumulate on the scraper and the holder. Then, since the deposit is plugged up in the holding means of the holder and solidified, the scraper and the holder are fixedly attached to each other. Accordingly, at a time of replacing the scraper which is consumed by using for a long time, it is hard to extract the scraper from the holder.
Further, according to the scraper of the second EP, the lower portion of the supporting member is held by the holding means of the holder, the upper portion thereof is stood up from the holding means and the scraping portion at the upper end thereof is come into contact with the running conveyor belt. Accordingly, a moment is produced on the supporting member toward a returning direction of the belt. The supporting member is fixedly attached to the yieldingly deformable resilient board and is opposed to the moment through the resilient board. However, since the resilient board may be compressed and deformed by the supporting member at that time, the supporting member is finally forced to become an inclined posture inclining toward the belt running direction from an erect posture. Accordingly, a biased abrasion is produced in the scraping portion. Further, since the conveyor belt does not generally run at a uniform manner but runs with vibrating at a wavy manner, compression of the resilient board are repeated. As a result, the supporting member vibrates between the erect posture and the inclined posture so that the biased abrasion in the scraping portion becomes remarkable.
Further, when the supporting member vibrates with repeating the compression of the resilient board as mentioned above, a tiredness of the resilient board is invited at an early time so that there is a risk that a crack is produced in the resilient board. Particularly, a crack is easily produced at the hinge portions formed between the adjacent supporting members which are independently vibrated to each other. When the hinge portions are separated by such a crack, a gap is produced between the scraping portions in the adjacent supporting members so that there is a risk that the scraped leavings of material is plugged up there.